Application of subpopulation theory to evaluation of DNA evidence

The strength of any evidence can be assessed using a likelihood ratio (from Bayes' point of view). This is the ratio of the probabilities that the evi dence would have been obtained given that the suspect is guilty and innocen t, respectively. This, in turn, depends upon the probability that a match w ill be produced if the suspect is innocent. An essential population genetic s parameter is the 'coancestry coefficient', or theta, or F-ST, which is th e correlation between two genes sampled from distinct individuals within a subpopulation. In this paper, theta coefficients for the southern Polish po pulation were calculated fur three loci of forensic interest: TH01, TPOX an d CSF1PO. Three small southern Polish subpopulations of different ethnic or igin were analysed. The results suggest that values of theta appropriate to forensic applications are quite small in the southern Polish population (t hey vary in the range of 0.002 to 0.013), and the value of theta=0.03 sugge sted by the National Research Council is too conservative for the defendant . (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.